I have read your question,
Generally Synthriod (= Levothyroxine
Sodium ) is prescribed for hypothyroidism
patients just as in your case . Though the drug is quite effective it does have few side effects and amongst them hair fall
is prominent , yet the hairfall is generally a temporary effect and it occurs because your body is adjusting to the medication. This drug does not have any high-risk side effects so you need not worry much.
Since you have said that you have been using the drug since 6 years I think that is a lot of time and as the hair fall problem still persists , I recommend you to consult the doctor who prescribed you this medicine for more clarity.
As it comes to natural treatments for hair fall , applying amla (=indian gooseberry oil ) does tackle this problem effectively and also I suggest you to have a good diet and eat vitamin C
rich foods ,drink plenty of water for good results with in weeks.
I hope this helps you and wishing you a good health,